Intravascular ultrasound (IVUS) imaging systems have been designed for use by interventional cardiologists in the diagnosis and treatment of cardiovascular and peripheral vascular disease. Such systems enhance the effectiveness of the diagnosis and treatment by providing important diagnostic information that is not available from conventional x-ray angiography. This information includes the location, amount, and composition of arteriosclerotic plaque and enables physicians to identify lesion characteristics, select an optimum course of treatment, position therapeutic devices and promptly assess the results of treatment.
Such IVUS systems generally include an IVUS device having one or more miniaturized transducers mounted on the distal portion of a catheter or guide wire to provide electronic signals to an external imaging system. The external imaging system produces an image of the lumen of the artery or other cavity into which the catheter is inserted, the tissue of the vessel, and/or the tissue surrounding the vessel.
Before the development of less invasive approaches, the principal mode of treatment for occluded arteries was bypass surgery and, in the case of occlusions in the coronary arteries, coronary artery bypass surgery. Coronary artery bypass surgery is a highly invasive procedure in which the chest cavity is opened to expose the heart to provide direct surgical access to the coronary arteries. The procedure also includes the surgical removal of blood vessels from other locations in the patient's body (e.g., the sapheneous vein) which then are grafted surgically to the coronary arteries to bypass the occlusions. The recuperative period is lengthy with considerable discomfort to the patient.
The use of less invasive, catheter-based, intravascular techniques has developed for several decades and may be considered as the preferred mode of treatment for those patients amenable to such treatment. Typically, the intravascular procedures, such as angioplasty, atherectomy, and stenting require preliminary navigation of a guidewire through the patient's arteries to and through the occlusion. This guidewire, so placed, serves as a rail along which catheters can be advanced directly to and withdrawn from the target site. Total occlusions often cannot be treated with such minimally invasive intravascular approaches because of the inability to advance a guidewire through the stenosis. Typically patients with such occlusions have been treatable, if at all, by bypass surgery. Although in some instances, physicians may be able to force a guidewire through a total occlusion if the occluding material is relatively soft, attempts to force the guidewire through can present serious risks of perforating the artery. Arterial perforation can be life threatening.
As noted above, recently techniques and systems have been developed to visualize the anatomy of vascular occlusions by using intravascular ultrasound (IVUS) imaging. IVUS techniques are catheter-based and provide a real-time sectional image of the arterial lumen and the arterial wall. An IVUS catheter includes one or more ultrasound transducers at the distal portion of the catheter by which images containing cross-sectional information of the artery under investigation can be determined.
IVUS catheters typically include a distal portion that is more flexible than the proximal portion. The stiffer proximal portion provides some rigidity that may aid and simplify advancing the catheter into the patient by pushing the catheter from its proximal portion along the guidewire in the patient. The more flexible distal portion is configured to wind through more tortious vasculature, such as a patient's coronary artery, than the proximal portion. A flexible distal portion may decrease the likelihood of tissue damage as the catheter advances along the guidewire.
Because of the relatively large difference in stiffness, the intersection of the proximal and distal ends of the IVUS catheter may be prone to bending or kinking. Accordingly, when the proximal portion of the IVUS catheter is pushed to advance the catheter through the patient's vasculature, in some instances, the catheter can bend or kink. In some of these instances, a kinked catheter may no longer be suitable for completing the procedure or it may present health risks to the patient. Accordingly, in some cases, it must be withdrawn from the patient, discarded, and replaced with a new catheter. Conventional catheters lack the distal transducers discussed above that are included in imaging catheters. In order to communicate images or other data from the transducers to an image display system, electrical cables extend form the transducer through the catheter. Accordingly, the intersection of the proximal and distal portions should not only withstand introduction to the patient without being damaged, but should accommodate the cable in a way that does not interfere with standard operation of the IVUS or other imaging catheter.
Accordingly, there remains a need for improved devices, systems, and methods for visualizing vessels having a severe blockage or other restriction to the flow of fluid through the vessel. The present disclosure addresses one or more of the problems in the prior art.